July 10 (Bloomberg) -- John McCain has run for president twice, gone through four campaign managers, written five books and delivered hundreds of speeches. The one constant: Mark Salter, the Arizona senator's longtime aide and alter ego.

Salter, 53, is his most trusted adviser, traveling companion, image-shaper, sounding board, wordsmith and defender. He weighs in on almost every campaign decision, and in McCain's absence, even speaks for the presumptive Republican nominee.

``He's like a brother,'' said McCain, 71. ``There's no one closer to me in my life, besides my wife and kids.''

No president or potential president has had such a close relationship with an aide since John F. Kennedy relied on the counsel of his brother Robert Kennedy and speechwriter Theodore Sorensen, said Fred I. Greenstein, a historian at Princeton University in New Jersey.

Salter can read McCain's moods -- and anticipate his reactions and needs -- more keenly than anyone, allowing him to survive two shakeups of the campaign staff within a year.

It was Salter who persuaded McCain to take the offensive on the economy. He urged the candidate to emphasize the expertise he acquired as chairman of the Senate Commerce Committee, and suggested grouping McCain's wide-ranging proposals for U.S. energy independence under a single label, Lexington Project, a reference to a battle of the War of Independence.

Combative Approach

There is a downside to this comradeship, however, most notably because Salter's combativeness at times reinforces McCain's reputation for a hot temper.

When a May Newsweek article portrayed Republican campaign tactics in a negative light, Salter crafted a 1,289-word critique that called the piece ``scurrilous'' and sent it to the magazine without his boss's review.

In 2006, after the collapse of an effort by Barack Obama, now the presumptive Democratic presidential nominee, to work with McCain on lobbying and ethics, Salter wrote a letter on behalf of his boss accusing the Illinois senator of ``disingenuousness'' and ``self-interested partisan posturing.''

``Mark's kind of touchy about John,'' said Joe McCain, the senator's younger brother. ``Nobody is more loyal. He'd literally fight for John.''

Salter did just that in 1992 when an intruder caused a disturbance in McCain's Senate office. Salter escorted the man out.

`Fought Back'

``He slugged me and I fought back,'' Salter said. He held the man down until Capitol Police arrived.

Beyond protecting his boss from pests and menaces, Salter also is involved in most decisions, said Charlie Black, a senior McCain adviser.

Salter is ``a walking encyclopedia'' on ``everything John's ever done, every policy John took, every speech John made,'' Black said.

``There aren't key meetings that don't include Mark,'' said Carla Eudy, who supervises McCain's schedule.

After the fight between McCain and then-Texas Governor George W. Bush for the Republican nomination in 2000, antagonism between the candidates' advisers made it easier for McCain to oppose Bush, 62, on a range of issues, including his tax cuts.

`A Little Raw'

``Some of us were a little raw,'' Salter said.

Mark McKinnon, a former Bush media consultant now advising McCain, said Salter's role equals that played by three people in Bush's campaign: Karen Hughes, who could ``tell the candidate things he doesn't like to hear''; Dan Bartlett, who knew ``every detail of the candidate's history''; and speechwriter Mike Gerson, who could ``forge and articulate his message.''

This combination makes Salter at least as influential with McCain as Karl Rove was with Bush, who referred to his adviser as the ``architect'' of his White House campaigns.

Examples of this influence abound. When McKinnon wanted to use footage of McCain as a prisoner-of-war for an ad, it was Salter who persuaded the candidate to agree.

When McCain prepared to launch a ``biography tour,'' Salter came up with a catchier theme: the ``Service to America'' tour -- a reference to McCain's record of public service since age 17, when he enrolled at the U.S. Naval Academy.

Age Concerns

To allay concerns about McCain's age -- he turns 72 next month -- Salter urged him to talk up his mother, Roberta, who at 96, remains active.

Salter was born in Iowa. His father, a Korean War veteran, was a traveling salesman; his mother a schoolteacher. After graduating from Georgetown University in Washington, Salter wrote speeches for United Nations Ambassador Jeane Kirkpatrick. He joined McCain's Senate office in 1989 and became chief speechwriter, then chief of staff.

Salter and his wife, Diane, who was McCain's scheduler, have two daughters. They spend summers at a house in Maine they bought with royalties from the best-selling books Salter wrote with McCain, including his 1999 memoir ``Faith of My Fathers.''

Salter's intimacy with McCain would ``be dangerous if Mark wanted their relationship to be exclusive,'' Black said. ``But he doesn't; he's a great team player.''

McCain said the alter-ego label ``does a disservice to Mark.'' Salter said it was ``a myth'' because his advice is rejected ``all the time.''

Still, no one disputes their bond.

``What Salter does so exquisitely is to tell John McCain what he needs to know,'' said Kenneth Duberstein, President Ronald Reagan's White House chief of staff, ``not necessarily what he wants to know.''

To contact the reporter on this story: Edwin Chen in Washington at echen32@bloomberg.net.

Last Updated: July 10, 2008 00:01 EDT